A Study of Cu-Mn-Al Alloys with High Temperature Coefficient of Electrical Resistivity

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  • 高い電気抵抗の温度係数を有するCu-Mn-Al系合金
  • タカイ デンキ テイコウ ノ オンド ケイスウ オ ユウスル Cu Mn Al

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Investigation has been made into the electrical resistivity ρT and its mean temperature coefficient Cf at temperatures from 293 to 373 K, the electrical resistance at elevated temperatures from room temperature to 1073 K, and the melting point for Cu-0-75 at%Mn-0-50 at%Al alloys in the air-quenched state. The alloys show a complicated variation near ρ293 at 293 K with Mn and Al concentrations, respectively. Generally, ρ293 in the composition in 25 at%Al shows a lower value. To be more specific, its value increases slightly at first and monotonously after showing a minimum value lower than 0.3 μΩ·m at 20-31 at%Mn with increasing Mn concentration, and then reaches the highest value of 2.0 μΩ·m at 70 at%Mn. On the other hand, Cf at 293-373 K shows a maximum value higher than 5000×10−6 K−1 near the composition of ρ293 minimum, and contours of equivalent values of Cf take the form of a long elliptical shape which expands with the Mn concentration.<BR>When the temperature is elevated, the electrical resistance Δρ⁄ρ273 vs. temperature T curves of the Cu-Mn-25 at%Al alloys show a very complex change with the Mn concentration. In general, the heating and cooling curves do not agree with each other. However, near the composition of 25 at%Mn, the Δρ⁄ρ273−T heating curve agrees well with the cooling curve at a temperature lower than the magnetic transformation point. This appears to be due to the reason that the electrical properties of the (αCu+T3+γ) and (γ+T3+βMn) phases which exist in the lower temperature range are balanced.<BR>When quenched in air at the cooling rate of 1.75 K·s−1 after heating at 1073 K for 3.6 ks, a Cu-22.5 at%Mn-25.0 at%Al alloy exhibits ρ273 and Cf of 0.26 μΩ·m and 4100×10−6 K−1, respectively, and its product ρ·Cf is 1066 pΩ·mK−1 which is 2.7 times as large as that of the practical element material being used for temperature sensors. In addition, this alloy has many advantages as follows: The linearity of electrical resistance at temperatures lower than 400 K is good; the electrical properties are scarecely changed after heating for a long period less than 100 ks; the melting point is as low as 1200 K; the material is inexpensive.<BR>Except for their poor antioxidation and non-workability, the alloy is a very promising element material for use in low-temperature sensors of a relatively low temperature range.

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